Super Smash Bros. Brawl is considerably co-op, it's not partial in the line of Mario at all.
It's 2 player co-op though, not 4 player.
Left 4 Dead might get split-screen co-op on 360, but I highly doubt it.
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )